With CA (Carrier Aggregation) stipulated in LTE (Long Term Evolution) Release-10, it is possible to realize high throughput by performing simultaneous communication while using a CC (Component Carrier) #1 and a CC #2 under the same radio base station eNB as shown in FIG. 12(a).
Meanwhile, “inter-eNB CA (or Inter-node UP aggregation)” is being studied in LTE Release-12, which is intended to realize high throughput by expanding the CA according to LTE Release-10 such that simultaneous communication can be performed by using a CC #1 and a CC #2 under different radio base stations eNB#1 and eNB#2 as shown in FIG. 12 (b) (see Non-patent document 1).
If a single radio base station eNB cannot house all the CCs used by one UE, for example, it is necessary to perform the above-mentioned “Inter-eNB CA” in order to realize the throughput comparable to that of LTE Release-10. Here, a possible case is illustrated in FIG. 13 where a radio base station MeNB serves as an anchor node and transfers a PDCP-SDU (Packet Convergence Control Protocol-Service Data Unit), which is transmitted by a gateway device S-GW, to any of a mobile station UE and a radio base station SeNB in order to perform the “Inter-eNB CA”.